Windows (Mac, Android, iOS coming soon): There are a ton of online syncing and storage services, but not all of them locally encrypt your data for higher security. Just out of limited beta, Tresorit is a new Dropbox alternative with client-side encryption. The company offers 5GB of free space, but for a limited time Lifehacker readers can grab 50GB free for life.

Tresorit's biggest selling point is the strong security. Your files and folders are encrypted before they're uploaded to the cloud. To get technical about it:

Files are encrypted with AES-256 before being uploaded to the cloud. Additional security is provided before upload by HMAC message authentication codes applied on SHA-512 hashes. Encrypted files are uploaded to the cloud using TLS-protected channels.

The company is also putting its money where its mouth is: On April 15, Tresorit is inviting the world's hackers to try to break its encryption and win $10,000. So Tresorit is pretty confident in its security claims.

The Windows software (Mac, Android, and iOS versions coming before June) is also really easy to use. You can select any folder to be synced (as a "Tresor"), share folders with other users, and also adjust permissions of shared folders by user.

On the downside, there's no web-based access for your files, people you share folders with will also need the software installed, and it takes a few seconds longer for your synced files to appear on another computer (probably because of the encryption that has to happen first). Other Dropbox alternatives with client-side encryption, SpiderOak and Wuala, have more features, but Tresorit's interface is a lot more user-friendly. And it's hard to beat 50GB of free encrypted space.

If you want to try it out, you'll need to register via the link below to get the 50 gigs free. This offer is good until May 20.

Update: Some people are reporting only getting 5GB. Tresorit has fixed the glitch, so it should work fine now, but if you were one of these people, email support@tresorit.com and they'll set you up with the 50GB. Also, you can follow @tresorit on Facebook or Twitter to be notified when Mac and mobile apps are available.